On a suburban road or expressway, a continuously variable transmission runs mostly in overdrive (overdrive transmission ratio). And the overdrive transmission ratio is the most frequently used ratio in total driving. Fuel economy performance on suburban roads and expressways can therefore be improved by installing a direct coupling mechanism and implementing overdrive in a direct mode through the direct coupling mechanism.
When a belt-type transmission is operating in overdrive, the winding diameter on the driven pulley side is reduced and the ring bending stress is high, so that the service life of the belt can be improved by driving with the most frequently used overdrive transmission ratio directly coupled. However, even when no torque is being transmitted, the idle rotation of the belt and pulleys causes torque loss and ring bending fatigue. The belt and pulleys must therefore be put in a non-rotating state during direct coupling.
Regarding this point, Patent Reference 1 teaches an automatic transmission apparatus comprising a continuously variable transmission having a drive pulley connected through a first clutch to an input shaft connected to a power source mounted in a vehicle, a driven pulley connected through a second clutch to an output shaft connected to driven wheels and an endless flexible member wound around the drive and driven pulleys, and, arranged in parallel to the continuously variable transmission, a (chain or gear type) direct coupling mechanism that directly connects the input shaft and output shaft and transmits rotation of the input shaft to the output shaft at a fixed (predetermined) transmission ratio, which automatic transmission apparatus is configured to enable establishment of a first power transmission system by means of the continuously variable transmission or a second power transmission system by means of the direct coupling mechanism.
The automatic transmission apparatus of Patent Reference 1 is configured to connect the direct coupling mechanism establishing the second power transmission system through a third clutch, connect the first clutch and the second clutch and disconnect the third clutch when establishing the first power transmission system, and connect the third clutch and disconnect the first clutch and the second clutch when establishing the second power transmission system.